The present proposal outlines a group of long-term projects requiring a modern resonance Raman spectrometer to examine a group of proteins containing a variety of chromophores. Applications of the instrument being requested include: (1) structural and mechanistic studies of the molybdenum center of xanthine oxidase and arsenite oxidase; (2) investigations of the heme centers of chicken liver sulfite oxidase, cytochrome c553 of A. faecalis, and thiosulfate reductase and (assimilatory) sulfite reductase from D. vulgaris; (3) structural studies of the iron-sulfur centers of arsenite oxidase, trimethylamine dehydrogenase and sulfite reductase; (4) characterization of the oxidized and semiquinone forms of the flavodoxins from D. vulgaris and Clostridium MP, and the electron-transferring flavoprotein from the pseudomonad W3A1; investigation of the effects of systematic site-directed mutagenesis on the flavin-protein interactions in the above lavodoxins; and (5) characterization of the effects of site-directed mutagenesis on the chromophores of photosystem II of higher plants. Together these projects constitute a major application of resonance Raman spectrometry that would greatly enhance the basic research capabilities of an extended group of scientists interested in spectroscopic studies of proteins. The proposed research constitutes essentially complete utilization in terms of both time and capabilities of a modern, versatile resonance Raman spectrometer.